The present invention regards an exhaust arrangement for an internal combustion engine.
Exhaust gas formed in the combustion of fuel in an internal combustion engine contains a proportion of undesirable substance such as nitrogen oxides (NOx), carbon monoxide (CO), un-burnt hydrocarbons (HC), soot, etc. . . .
To reduce air pollution, vehicles are therefore equipped with various systems that deal with undesirable substances in exhaust gas.
A common exhaust gas treatment is a so called selective catalytic reduction (SCR). Exhaust gas wherein ammonia is added as a reducer is treated in a specific catalytic converter where nitrogen oxides are converted into water and nitrogen which are both non toxic substances. Ammonia is introduced in the form of urea in an aqueous solution from which ammonia is obtained through hydrolysis. Urea is usually nebulised in the exhaust gases upstream of the catalytic converter. To this end, a urea injector is fitted on the exhaust line upstream the catalytic converter.
One of the key elements in a successful exhaust gas treatment in an SCR system is a homogenous mixing of the additive—in this case, urea droplets—in the hot exhaust gases. If the urea is insufficiently mixed in the exhaust gases, there is a risk of urea crystallisation. This has a detrimental effect on the NOx reduction that takes place in the catalytic converter and ultimately untreated NOx are rejected in the air as the reduction reaction that occurs in the catalytic converter is incomplete.
A mere injection of urea in the exhaust gases is largely insufficient to provide a homogeneous mixing of urea droplets in the flow of exhaust gases. This is why, in engines equipped with a SCR catalytic converter, the exhaust line can include a mixer that creates turbulences in the otherwise largely laminar exhaust flow and thereby encourages a homogenous mix of urea droplets in the exhaust gases.
Although the effect of the mixer is beneficial to an efficient working of the SCR catalytic converter, it may also be detrimental to engine efficiency and especially fuel consumption as the mixer hinders the exhaust gas flow.
Another point where exhaust gases are concerned relates to exhaust brakes.
An engine, generally a diesel engine, that powers an industrial vehicle such as a truck can be commonly equipped with an exhaust brake. Existing exhaust brakes can be of different design but operate on the principle of creating a back pressure in the exhaust manifold. An exhaust brake closes partially or totally the flow of exhaust gas that is released by the engine cylinders after combustion. By doing so, the exhaust gases are compressed in the exhaust manifold and in the engine cylinder. The exhaust back pressure is used to counteract the motion of the piston engine and then helps to slow down the vehicle. Although it is beneficial to improve additive homogenization in exhaust gas so as to improve depollution treatment efficiency and although it is desirable to have some exhaust gas restriction to help slow down a vehicle especially a heavy vehicle, it is also desirable to avoid any disruption in the flow of exhaust gas. In other terms, any device added onto an engine exhaust line such as for example an exhaust gas mixer and an exhaust brake ultimately impairs engine efficiency and tends to increase fuel consumption.
It therefore appears that there is room for improvement in the way exhaust gases are handled after they are generated in an engine cylinder and before they are treated in a pollution reducing device.
It is therefore desirable to promote homogenization of liquid additive in exhaust gas when an internal combustion engine is in an operative mode that ensures insufficient additive homogenization and to offer supplemental braking resource and to promote low fuel consumption.
It is also desirable to provide an exhaust gas arrangement that can be integrated into a vehicle architecture with minimal structural and functional disruption.
An aspect of the invention concerns an exhaust arrangement for an exhaust line having an exhaust gas treatment device and a liquid injection device located upstream of the exhaust gas treatment device; the said exhaust arrangement comprises a single moving element incorporating a throttling member having a closing surface at least substantially equal to the cross section of the exhaust line and, operatively connected to the said throttling member, a turbulence generating member; the said exhaust arrangement further comprises actuating means for controlling the position of the said moving element between a first position wherein the moving element is in a retracted position and creates a minimum backpressure in the exhaust line and a second position wherein the shutter member is in an extended position and creates a maximum back pressure; the actuating means can position the moving element selectively in at least one intermediate position between the said first and second positions wherein the moving element is in a turbulence generating position wherein the turbulence generating member intrudes at least partially into the exhaust line and creates turbulences within the flow of exhaust gas.
The invention therefore provides, according to an aspect thereof, an exhaust arrangement that is a single operational unit which therefore can be integrated into a vehicle architecture without substantial redesign to accommodate the said arrangement. Further the exhaust arrangement according to this invention combines two functional effects namely (i) creating turbulence in a flow of exhaust gas and (ii) at least partly shutting off the flow of exhaust gas depending on its position in an exhaust flow while being unobtrusive (and therefore without any impact on fuel consumption) when the vehicle operational conditions do not require either to create turbulence in the exhaust flow or to shut off the exhaust line.
According to an embodiment of the invention, the moving element is transversally mobile with respect to the exhaust line; the moving element is capable of displacement between a first extreme position wherein the moving element is in a fully retracted position and creates a minimum backpressure in the exhaust line and a second extreme position wherein the moving member is in a fully extended position and creates a maximum back pressure, or selectively in at least one intermediate position wherein the mobile element is in a turbulence generating position wherein the turbulence generating member intrudes at least partially into the exhaust line and creates turbulence within the flow of exhaust gases.
Preferably, the turbulence generating member extends from the throttling member.
Advantageously, the turbulence generating member has a surface at least equal to the section of the exhaust line so that the moving element can be set on a position wherein the entire section of the exhaust line is covered by the turbulence generating member. This promotes the creation of homogenate turbulence within the flow of exhaust gas.
It can be envisaged that the turbulence generating member can comprise an array of strips defining at least one opening. The exhaust gas that passes through the at least one opening changes from a laminar flow to a turbulent flow. in practical terms, the array of strips can comprise two sets of perpendicular strips.
In order to increase the turbulence in the flow of exhaust gas, at least one of the strips can be provided with a spoiler on the downstream side of the turbulence generating member.
Advantageously, the exhaust line is provided with a housing that accommodates the turbulence generating member when the moving element is in the second extreme position. This disposition makes it possible to entirely seal the exhaust line with the throttling member when the vehicle operational conditions require supplemental braking power.
Further, the throttling member can have a surface at least substantially equal to the section of the exhaust line; this feature of the invention makes it possible to substantially or fully seal the exhaust line and therefore to create a maximum back pressure.
In a further embodiment of the invention, the moving element is axially mobile within the exhaust gas flow path and is capable of displacement between a first extreme position wherein the moving element is in a fully retracted position and creates a minimum backpressure in the exhaust line and a second extreme position wherein the moving member is in a fully extended position and creates a maximum back pressure, or selectively in at least one intermediate position wherein the mobile element is in a turbulence generating position wherein the turbulence generating member intrudes at least partially into the exhaust line and creates turbulences within the flow of exhaust gases. To seal the exhaust line and therefore to create a maximum back pressure, the moving element can comprise a throttling element the surface of which equals the section of the exhaust valve and at least one protruding member extending from the throttling element.
The protruding member which generates the turbulence within the flow of exhaust gas can be comprised of an array of strips that extend perpendicularly from the throttling member.
So as to further enhance the turbulence created within the flow of exhaust gas, at least one the strip can be provided with a spoiler.
Besides, the exhaust line can be provided with a wall that surrounds the moving element when the said moving element is in a fully retracted position to maintain the flow of exhaust gas as laminar as possible when the moving element is in a fully retracted position.
The invention also concerns, according to an aspect thereof, an internal combustion engine, which includes an exhaust arrangement as above described.